L0301P21 - Integrative Tissue Metabolism
Liver *function adapts to a person’s state *stores and distributes nutrients **glucose - glycogen **fatty acids - triglycerides Adipose Tissue *composed of adipocytes *all over the body - particularly in abdominal region *stores fat in the form of TAG *very metabolically active *responds to hormonal stimuli *glycolytic pathway, beta-oxidation and CAC *chylomicrons - transports TAG in bloodstream from intestines to body tissue *VLDLs - transport TAG from liver into bloodstream to body tissue *glycolysis must be active for TAG synthesis Mobilisation of TAG *breakdown of TAG to release glycerol and fatty acids *fatty acids released into the blood stream and bind to albumin *glycerol released into the blood stream and taken up by the liver and used to synthesise glucose Metabolism of Fatty Acids (β-oxidation) *cleaving off 2C units at a time as acetyl CoA *use NAD+ and FAD —> NADH and FADH2 *acetyl CoA goes into the citric acid cycle *NADH and FADH2 go to electron transport chain Skeletal Muscle *counts 20-90% of total O2 consumption *adapted to work in an intermittent fashion *sources: **light activity or rest ***fatty acids ***ketones ***glucose **bursts of heavy activity ***muscle glycogen ***creatine phosphate At rest *fatty acids - major source of energy (>80%) *obtained from circulation as free fatty acids bound to albumin or associated with chylomicrons or from the liver associated with VLDLs *ketones from the liver can be oxidised and degraded to acetyl CoA Moderately active *glucose from glycogen stores of liver *fatty acids and ketones Short bursts of energy *ATP reserve *creatine phosphate **a high energy storage compound **rapidly regenerates ATP during first few minutes of energy requirement **originates from amino acid, glycine Extremely active *blood flow often cannot provide sufficient oxygen and fuels fast enough for aerobic respiration to occur, so anaerobic respiration occurs instead *stored muscle glycogen —> lactate *lactate can be converted back to glucose through the Cori cycle of the gluconeogenesis Starvation *break down of proteins to produce amino acids which are taken up by the liver for gluconeogenesis to occur *alanine levels increase during starvation Heart Muscle *continually active unlike skeletal muscle *cannot undergo anaerobic fermentation *lack of oxygen can have major fatal consequences *fatty acids are the primary fuel *can also utilise glucose and ketones Brain *uses high amounts of energy to create electrical signals *has very high metabolism *no fuel reserves *relies primarily on blood glucose *in fasting conditions, can use ketones During starvation *brain can utilise ketones synthesised in the liver *as ketones can cross cell membranes (blood-brain barrier) readily *reduces need to maintain blood glucose and slow down the rate of protein degradation Ketone Bodies *acetyl CoA from oxidation of fatty acids converted to ketone bodies *exported to other tissues *acetone, β-hydroxybutyrate, acetoacetate Red Blood Cells *relies entirely on glucose *no organelles thus cannot oxidise fatty acids *metabolise glucose by anaerobic pathways **glycolytic pathway **pentose phosphate pathway (do not need to learn the pathway) *highest rate of glucose utilisation (anaerobic needs 16x more glucose to get the same as aerobic respiration) Pentose Phosphate Pathway *produces NADPH from glucose Summary Diagram